bonds in proteins, the approach has been extended to methyl groups
resulting in sharp NMR signals for very large proteins exceeding 1000 kDa
in size. Since amino acid side chains spin rapidly about their axes, the
magnetic interactions are effectively decreased. This application for methyl
groups has been used to examine the structure of the 20 S proteasome CP
(Spranger & Kay 2007). The NMR structure confirms the previously deter-
mined X-ray diffraction structure showing the presence of two heptameric
rings stacking together to form a barrel. The use of the methyl-based TROSY
technique provided information about 100 methyl groups found in the
isoleucine, leucine, and valine amino acid residues. The successful deter-
mination was aided by the overall symmetry of the protein as many
spins were magnetically equivalent, thus reducing the total number of
unknown interactions.
CHAPTER 16 MAGNETIC RESONANCE 355
COSY R90 L64 E119TROSYCOSY R90 L64 E119TROSY120125115125120115COSY
R90E119L64TROSY98 ω 2 (^1 H) [ppm]ω 1 (^15 N) [ppm]
ω 1 (^15 N) [ppm]
116 114 120 118 130 128
ω 1 (^15 N) [ppm]8.28.4 8.0 7.0 6.8 6.6 9.6 9.4 9.2
ω 2 (^1 H) [ppm]
R90E119L64Figure 16.10Comparison of TROSY and COSY spectra of a 110-kDa protein, 7,8-dihydroneopterin
aldoase. From Riek et al. (2000).